The design of a communication network or system involves evaluating physical constraints, for example, the characteristics of a given communication channel, and system constraints, for example, the available bandwidth per channel, in order to achieve a network with desired performance characteristics, such as reliability of the information received. Cellular systems typically require low throughput delay of information and high reliability of information transfer and high capacity while restricting the bandwidth of each cellular frequency band.
Current wireless networks utilize multiple access techniques which multiplex users together in order to efficiently utilize network resources. In particular, these networks use either TDMA (time-division multiple access) with FDD (frequency-division duplexing) as in the pan-European GSM system (now also known as Global System for Mobile Communication) and the North American IS-54 system, or a variant, TDMA/TDD (time-division duplexing), as in the Digital European Cordless Telecommunications (DECT) system. See D. J. Goodman, "Second Generation Wireless Information Networks," IEEE Trans. Veh. Tech., VT-40, No. 2, pp. 366-374, May 1991.
For the multiple access systems described here, frames of time are the basic transmission unit. Each frame is divided into a plurality of slots of time. Some slots are used for control purposes and some slots are used for information transfer as described below. The information is transmitted during slots in the frame where slots are assigned to a specific user. Throughout this disclosure, it is understood that the term "information" refers to data representing speech, text, video or other digital information.
Other multiple access techniques, such as PRMA (Packet Reservation Multiple Access) and R-ALOHA (Reservation ALOHA), recognize the bursty nature of speech packets and increase system capacity by having a reservation mechanism for time slots. See D. J. Goodman, R. A. Valenzuela, K. T. Gayliard and B. Ramamurthi, "Packet Reservation Multiple Access for Local Wireless Communications," IEEE Trans. Comm., COM-37, No. 8, pp. 885-890, August 1989; and S. S. Lam, "Packet Broadcast Network--A Performance Analysis of the RALOHA Protocol," IEEE Trans. Comp., COMP-29, No. 7, pp. 596-603, July 1980. Although able to support a large number of users on a given channel bandwidth, these approaches have limited operating ranges, and in the case of PRMA, perform poorly under low delay constraints. In addition, PRMA techniques rely on actual speech transmission, that is, the user must be actively speaking, to allocate slots instead of relying on a separate control mechanism for allocating slots. This assignment method leads to collisions between packets of data and thus increases delay and reduces throughput. Other systems recognize that in a two-way conversation, it often occurs that only one user is active, thereby making it possible to obtain a high statistical multiplexing gain even with a low number of users when information from both conversation paths are multiplexed onto a common channel. See L. M. Paratz and E. V. Jones, "Speech Transmission Using an Adaptive Burst Mode Technique," IEEE Trans. Comm., COM-33, No. 6, pp. 588-591, June 1985; and S. Nanda and O. C. Yue, "Variable Partition Duplexing for Wireless Communications," GLOBECOM '91, pp. 32.6.1-32.6.7. However, such systems have typically been used to dynamically vary bandwidth assigned to two parties in a single conversation (duplex voice link). This reduces speech quality when both parties are talking simultaneously or when their speech overlaps. In addition, managing slot assignment is difficult since fractional slot assignment is necessary. Thus, there is a need for a multiple access system capable of providing high capacity, high quality and low delay communications, particularly for wireless personal communications systems competing with wired systems.